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The axes of energy

Figuring out how to meet the world’s demand for energy involves choosing between two complex, or dare say “inconvenient” formulas: Cost optimization based on the cheapest forms of energy available vs. the risk of pumping the resulting carbon dioxide into the atmosphere.

The cost optimization formula is relatively easy: The world is awash in oil, coal and other forms of fossil energy; and the supply will last for all of our lifetimes.

The carbon formula is a bit stickier: Based on energy consumption projections, the amount of carbon dioxide in the atmosphere will at least double by 2050. Carbon dioxide is the principle contributing “greenhouse” gas that prevents heat from escaping the planet. And there is enough fossil fuel left on the planet to pump at least five times the amount of carbon dioxide currently in the atmosphere.

Dr. Nathan S. Lewis, a professor of chemistry at Caltech, presented these issues at the May 15 National Energy Symposium at USC.

A major problem with the carbon-risk formula is the unknown. No one knows what a safe or unsafe level of carbon dioxide is, Lewis said. It could be just above what it is now, or it could be double or triple.
“Whether or not this will be a problem or has no effect at all, we don’t know. There are about six major climate models out there, all differing in detail, which means in detail at least five of them must be wrong,” he said.

Added to the element of the unknown, any damage caused by carbon dioxide is irreversible on a human time scale. Carbon dioxide remains in the atmosphere for more than 2,000 years. At the rate of world energy consumption, carbon dioxide is accumulating in the atmosphere much more quickly than it is being destroyed.

“We don’t know how to fix the changes [to the ozone lawyer] if we don’t like what we get. We only get one shot. It’s a one shot experiment. And at the current rate of energy consumption, we’re facing that problem within the next 20 years. If we don’t build the infrastructure very soon, the carbon dioxide will accumulate to these levels and stay there for a long, long time,” Lewis said.

“So the question is, in this one-shot experiment, how comfortable do we feel doing it? And do we have the leadership to deal with it?”

Running on empty?

Just how much oil is there, and when will we run out of it?

“The president said we are ‘addicted to oil’; and by implication, we should kick the habit. The question is how and whether we should,” Lewis said.

Estimates of when the supply of oil runs out range from 40-150 years. (See Lewis's Power Point Presentation.)

“We have no idea how much there really is,” Lewis said. “Discovery has never stopped.”

If oil did run out, there is plenty of coal to take its place. The estimated supply of coal ranges from several hundred years to three centuries. Lewis noted that during World War II, when the Allies cut off the supply of oil to Germany, Germany quickly switched to coal and converted it to gas to fuel its war machine.

“We’ve got plenty of coal, and so does China. We could be energy independent if we wanted to,” Lewis said.

Another potential source of energy could be captured from the methane ice sheets located off of the continental shelves, which encompass more than all of the other fossil energy sources combined.

“We have abundant sources of fossil energy on the planet. At the current consumption rate, we have ample fossil energy for many centuries,” Lewis said. “How long do we have until it runs out? We won’t know until we get there.”

The cost axis

About 85 percent of all energy consumption – including the generation of electricity – comes from oil, gas and coal. The world consumes about 13 trillion watts of energy every day.

In terms of cost, burning coal is presently the cheapest way to make electricity. Solar is at least six times higher, largely due to the cost of building the infrastructure necessary to capture solar energy.

Producing electricity from nuclear power is in the range of double the cost of coal. The primary reason is the high cost of siting and constructing new plants, which are politically unpopular in the United States. .

“Fossil energy is the lowest-cost energy we have on the planet today,” Lewis said. “Using the axis of optimization based on cost, it’s pretty clear cost optimization will lead us to rely almost exclusively on fossil energy for decades to come.”

World energy consumption

Projecting the amount of carbon dioxide humans will produce from burning fossil fuels is a complex process that involves calculating population growth, growth in productivity, and energy efficiency.

Projecting that the world population will grow to 10 billion people by the year 2050, and factoring in a 1.6 percent annual growth of per capita gross domestic product, demand for energy climbs steadily. But there is also a trend toward energy efficiency: Globally, the world is consuming less energy per GDP.

“If we continue to save about 1 percent per year and continue to do so for 50 years, bringing us as near to the limit of what a technologically reasonable society can conceive of; and if we know the number of people; and we know energy consumption per GDP; and we know GDP growth, then we know the energy demand,” Lewis said.
Plugging the numbers into this formula, world energy demand will about double by 2050. This will mean the world will need about 28 trillion watts by mid century, compared to 12 trillion watts in 1990.

“There has never been a year on the planet than we’ve used less energy than in the year before,” Lewis said. “Population growth and GDP growth will conspire to increase energy demand.”

The carbon axis

Based on the projected energy demand, the amount of carbon dioxide in the atmosphere will at least double by the year 2050 – even if technology leads to the use of the cleanest fossil energy sources available.

What will this mean for the planet? “We won’t know until we open the door in 2050,” Lewis said. “We know at the rate we are going, assuming we conserve energy like never before, and if we have a pure natural gas economy, the carbon dioxide levels within our lifetime will be at least twice as high as anything that has been on our planet in the last million years.”

From the ice core records, the amount of carbon dioxide in the atmosphere has never been higher than 300 parts per million for the past million years. The level of carbon dioxide has experienced downward swings of 100-200 parts per million over that time period.

“These swings have been correlated with, but have not necessarily been the causes of temperature changes that have repeatedly brought us into ice ages,” Lewis said. “Now the carbon dioxide levels are swinging upward by more than that, and we will watch to see what happens.

“We know that CO2 when burned goes into the atmosphere; and we know that half of it stays in the atmosphere, and about half is absorbed into the oceans; we know how much CO2 will appear as a result of burning fossil fuels; and furthermore we know that since there is no natural destruction mechanism, it will stay for 2,000 years,” Lewis said. “It all adds up.”

“We don’t know, except in a climate model, exactly what the outcome of that will be. We don’t have a definitive scientific proof, and we can’t do that because we can’t do the definitive scientific control of removing the carbon dioxide and seeing what the effect is. So we will always speculate to some extent about the effects. Some scientists say it could be a lot, some say a little. But we won’t know until we open the door in 2050, which will be the only time we will absolutely know the climate in 2050.”

The carbon axis, therefore, leads to a risk axis – the risk of emitting that much carbon into the atmosphere without knowing the outcome, and without having a way to fix it if the outcome is negative.

Possible solutions

The great technical challenge of the century is to develop energy sources that do not involve carbon dioxide as a byproduct, and to achieve this along the cost axis.

“Do we even have a clue as to how we would cost-effectively build enough carbon-free power within the next 50 years to even hold the CO2 levels to double what they have ever been on our planet in the last million years?” Lewis asked. “We don’t have the technology to do that now cost-effectively.”

Some possibilities to consider:  

  • Nuclear power – In order to hold CO2 levels to double over the next 50 years, the world would have to build 10,000 new nuclear power plants, Lewis said. But there is not enough uranium on earth to run that many reactors in perpetuity.
  • Clean coal using carbon sequestration – Carbon dioxide can be pumped into natural gas reservoirs where gas has been stored since geologic times, but there is not enough capacity there to hold all of the billions of tons of carbon produced by burning the earth’s coal. Carbon dioxide can also be pumped into underground brine aquifers, as is being explored as part of the U.S. Clean Coal Initiative. The has about 100 years worth of capacity to store carbon in brine aquifers. But preventing the carbon from leaking into the atmosphere would present another major technical challenge.
  • Hydrogen – Current methods of producing hydrogen involve either coal or natural gas, thus limiting the feasibility of a hydrogen economy.  


Renewable energy is the ideal “no carbon” solution, but developing a renewable energy economy would require significant technological breakthroughs to be both possible and cost-effective.

Energy from renewable sources – such as biomass, ethanol, and solar energy – is presently only a tiny fraction of the overall energy consumed. At the current growth rate for renewables, it will take a very long time for it to become significant.

These renewable resources contain the following maximum energy potential:

  • Hydropower – There is less than 1 terawatt worth of electricity left to harness from all of the lakes, rivers and streams of the world.
  • Wind – About 2-4 terawatts.
  • Biomass – About 5 potential terawatts, assuming rapid advances in agricultural technology to grow energy-producing crops.
  • Solar energy – More energy from the sun hits the earth in an hour than all of the energy consumed on earth in a year. But technology would have to find a way to capture the sun’s energy, store it, and do so cost-effectively.  

Strategy vs. tactics
The carbon axis vs. the cost axis

A tactical perspective on energy looks at the short term, while a strategic perspective looks at the long term. What changes should society make on a strategic level as opposed to a tactical level?

The world can rely on over a century’s worth of fossil fuels as the cheapest source of energy. The chief issues in acquiring fossil fuels are the tactics employed in obtaining it.

“Tactics include whether or not we fight a war; whether or not we have LNG plants; whether or not we use coal – those are all tactics,” Lewis said. “We have plenty of fossil energy, so if it’s the low-cost axis, that’s tactics optimized.”

The tactics involved in acquiring energy will not likely change much. “Humans have always fought wars over resources, and the future will be almost certainly no different than the past,” Lewis said. “In the long term, where there is energy to be had, humans will get to it.”

The risk axis requires factoring in unknowns over hundreds of years – far beyond the political cycle or even the human life cycle.

“A low-carbon economy requires that we depart from the low-cost axis and take into account NOW some risk that may or may not come. But if it comes, it would persist for at least 1,000-2,000 years,” Lewis said. 

If one assumes that carbon dioxide won’t pose a problem in the future, one ignores the potential risk.

“How much we are willing to pay to forestall the risk that if we accumulate that much carbon dioxide, we might get into a situation we have no way to fix?” he said.



Energy is measured in many different ways: barrels of oil; cubic feet of natural gas; kilowatt hours of electricity. Scientists use the common denominator of “joules” to measure energy, and the rate of energy consumption is watts. (A joule is the amount of energy it takes to move an approximately quarter-pound object one meter.)

“Energy is the currency of the world. It’s not dollars and cents, but the joule and the watt,” Lewis said.

Copyright 2006 The Communications Institute. All Rights Reserved.

Editorial Notes: You can view the video of Dr. Lewis's talk (71.2 MB; 1 hour 10 minutes in length). Much more information from the The Communications Institute's National Energy Project is online. Energy Bulletin also covered the conference. The talk given by Nathan Lewis at the conference is an abbreviated version of a talk he has given multiple times elsewhere. Lewis has a webpage devoted to the talk, with a summary, audio, downloadable transcript and slides. A Caltech page has a video of the talk: Powering the Planet: Where in the World Will Our Energy Come From?
In a Watson lecture, Nathan Lewis, Argyros Professor and professor of chemistry at Caltech, discussed what it would take for the world to turn away from fossil fuels and switch over to renewable energy. He outlined the hurdles that must be overcome in order to power the planet with abundant, clean, inexpensive energy in the 21st century. 67 minutes
What intrigues me about the presentation is that it provides a framework for thinking and discussion. It brings together energy demand, global warming, fossil fuels and alternative energy sources. Rather than getting hung up on specific technologies or problems, it provides a much needed global view. For the most part, the assumptions are explicit, so it is possible to criticize them individually. Several assumptions do deserve a critical eye. In an earlier posting, EB co-editor AF wrote:
We're told that Nathan Lewis buys into the the more optimistic projections of the world's international energy agencies regarding oil reserves. However, the perspective on renewables is supposed to be a real 'eye opener.' After seeing the first 40 minutes, I would have to agree with the recommendations -- it's good stuff, very dense. Lewis does not see an immediate problem with fossil fuel depletion, but instead focuses on the need to get develop carbon-neutral sources of energy in order to deal with global warming.
Lewis told an interviewer:
"If you look back in history," Lewis said, "there have been 30 years worth of [peak oil predictions] that have always predicted three or four years out from the time they were made that the peak was there. They haven't been right yet. ... There's no doubt we can make oil, liquid hydrocarbons, out of [natural] gas and coal, of which there are abundant resources."
In general, the experts at the energy symposium did not seem to be familiar with what the peak oil argument actually says, knowledgeable though they were about other energy issues. For example in one presentation, a speaker said that "cheap oil was coming to an end," but they didn't believe in peak oil. (As most EB readers know, peak oil = the end of cheap oil.) For more work by journalist Bruce Murray (who wrote the summary of Nathan Lewis's talk), see FACSNET (energy). Of special interest is a piece with BU Professor Robert Kaufmann on Hubbert's Curve and the world supply of oil. Another comprehensive picture of energy demand, global warming and energy sources was developed independently by computer scientist Bruce Hodge. The 58-slide presentation shows how several "wedges" (strategies) can mitigate climate change and replace our declining and polluting energy sources with renewable sources. The concept of stabilization wedges was described in Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies by Pacala and Socolow (Science, 13 Aug 2004). Also see an interview with Pacala. -BA

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